Demi Lovato attacked cyber-bullies who made fun of her sister.

The 22-year-old singer was horrified when her half-sister Madison De La Garza, 13, received online abuse after posting a video of them together and Demi was quick to hit back at the trolls.

Madison - who played Juanita Solis on 'Desperate Housewives' - told Seventeen magazine: ''Last year I got a ton of negative comments after I posted a Vine on Twitter where I was cooking with Demi. People made fun of me, saying I had a hunchback. Demi freaked and direct-messaged people to yell at them, and she tweeted at her followers to stand up for me.

''Sometimes I wish she wouldn't give people attention - I've learned not to - but when people hate on me, she can't really hold back. She's strong and she's a free spirit, and that's what I love about her.''

Although Demi is away a lot touring, Madison revealed her sister always makes time for her.

She explained: ''I think when people say they wish Demi Lovato was their sister, they don't realise how hard it is to be related to someone who's constantly away on tour. But she's good at making time for me.

''We text constantly, and whenever she sees a funny tweet, she'll screenshot it and send it to our family group message. My phone is constantly going off just from that. When Demi is home, our relationship is just like any sisters'. We get Froyo (frozen yoghurt) and watch the ID channel - we're obsessed - and we talk about anything and everything. I know I can trust her with it all.''